How a Simple Gas Leak Could Destroy Two Entire Buildings

The aftermath of a natural gas disaster can be unbelievably grim—sky-high sheets of flame, entire structures gone in seconds. The world got to see the destructive signature of a gas blast Wednesday in East Harlem, when a pair of five-story buildings exploded and crumbled into a fire-licked pile. At the most recent count, seven people died in the incident and at least 60 were injured.

Ron Lavezzo, fire-division chief for the Bay Area city of Millbrae, is a man familiar with gas-scented mayhem. He was among the first on the scene at the San Bruno pipeline explosion of 2010, a conflagration so fierce the media at first reported it as a plane crash that had set the "whole neighborhood on fire."

"After that thing happened,” says the 30-year firefighting veteran, “I started becoming very intimate with how many gas lines were in my district."

Gas disasters can occur in different ways with varying levels of damage, from shattered window glass to a screaming flame-jet that carbonizes rows of houses. Lavezzo described for Cities his own experience battling a titanic gas blaze and the kind of situations that could provoke a spectacular blowout like in New York:

What's the setup for a bad gas explosion?

Natural gas is conveyed over the land in pipes of different diameters and pressures. The problem begins when a pipe develops a leak or rupture due to aging infrastructure or construction work. In Lavezzo's experience responding to calls last year, the two causes broke down to about 50/50.

In the San Bruno calamity, a sizable and highly pressurized 30-inch transmission line operated by Pacific Gas & Electric suffered a major breach. A screaming eruption of fumes dug out an immense crater and threw a 28-foot-long section of heavy pipe about 100 feet away. The U.S. Geological Survey registered it as a small earthquake.

Nobody knows yet exactly what happened in New York. But Lavezzo says there are a couple of ways that gas escaping from smaller and less-pressurized urban lines, such as 8-inch mains, could do such significant damage. "If there are gas leaks into a house that's unoccupied, and it fills the house, now you've got a bomb," he says. Or if there's a pipe that has been leaking for a long time underground, and it fills up a storm drain or subterranean vault with a large amount of gas, that could also rock the block.

Not exactly, but many major cities sit atop huge networks of antiquated, fragile, and hard-to-work-on gas lines. Researchers recently detected an incredible 5,900 natural-gas leaks under Washington, D.C. In Los Angeles, NASA scientists are trying to figure out what impact such "fugitive emissions" might have on climate change. "There are millions of miles of little pipes that go from distribution stations to people’s houses," says one. A lot of them are degraded, and "the leaks can be very substantial."

The most troublesome sort of pipes are made from cast iron and can predate World War II. National Geographicexplains more:

The root of the problem is the cast-iron and wrought-iron pipe that gas companies used to build their distribution networks in many parts of the nation back in the early to mid-20th century. While strong, the iron pipes are vulnerable to corrosion, and their rigidity makes them susceptible to stresses, including pounding from construction and vehicle traffic above....

Utilities have replaced most of the old iron infrastructure over the past several decades. But according to the federal regulator, the U.S. Pipeline & Hazardous Materials Safety Administration, nearly 46,000 miles of iron mains and service lines to individual homes were still in place in 2012, the most recent year for which data is available. Even though only 2.6 percent of the nation's distribution lines are still made of cast iron, 11 percent of the incidents that caused accidents or fatalities have involved cast-iron pipes.

An investigation will determine if New York's blow-up was related to iron pipes. In San Bruno, a National Transportation Safety Board investigation established that the fire was caused by a section of line dating from the 1950s with defective welds. "They don't put welded pipe in anymore," says Lavezzo. "They put seamless."

Points of leaking methane in the District of Columbia, as detected in 2013 by Duke and Boston University researchers. (Duke University)

What can turn a gas leak into a gas conflagration?

San Bruno started as an eruption of swirling vapors, but once the gas hit a high-tension wire two blocks away that sparked, it became an all-consuming flamethrower. In a dense urban environment like Manhattan, a horde of other things could trigger an explosion.

A cigarette ember tossed into a sewer could do it, or exposed wires in a telecommunications manhole. In a residence, it could be a frayed electrical cord, glitchy outlet, broken light bulb, poorly wired light switch, or any kind of motor with brushes in it. "Arsonists are the best for finding these things for you," says Lavezzo. "They get away with [some crimes] because they know ignition sources are so prevalent."

The fire response after the East Harlem explosion. (John Minchillo / Associated Press)

Is it normal for gas accidents to utterly destroy a building?

No, it's extremely rare. But the incidents in New York and San Bruno serve as testaments to the unpredictable and terrifying power of serious gas failures.

In the majority of calls for gas leaks, firefighters respond only to shuffle around for an hour for a minor-or-nothing incident. In certain cases, utilities venting gas during tests provoke scads of false alarms; in others, a utility can shut down a minor leak by simply turning a valve.

Gas that builds up inside a confined area carries a lot of potential energy, though. It exerts pressure by just occupying the space, then exponentially more pressure when it explodes. "Because there's nowhere to vent itself, the explosion and the pressure knocks down everything in its way," says Lavezzo. The most common results are shattered windows and structural damage.

But not total disintegration. That has Lavezzo wondering whether the Harlem building was unstable in some way: a bad foundation, damaged supports, poor overall construction? Either way, a strong infusion of gas would be needed for this level of devastation, he thinks. "If it took down two 5-story buildings, that's a lot of gas unless somebody put some dynamite in it." Video footage of four-story flames suggest that, indeed, there was probably copious gas in the vicinity.

The San Bruno fireball also took out entire buildings, about three-dozen total. The scene was nightmarish: Of the eight people the disaster claimed, seven died within the first 10 minutes, says Lavezzo. "You could see 150 to 200-foot flames coming out of the ground and you could hear the rushing of high-pressure gas. I thought it was plane engines." A lake had formed over the burst pipe from a busted water main. Yet a column of unkillable fire shot through the water's surface, like a portal from hell.

"We were kind of up to our butts in alligators trying to contain it," Lavezzo says. "The flame was so hot some of the houses were incinerated, with nothing left but the front walkways and chimneys. It looked like the moon."

The gas fire in San Bruno, when the media still thought it was a plane crash.

Are there ways to tell if an explosion is imminent?

The putrid scent of mercaptan, a chemical added to natural gas and propane to make it detectable, is one warning sign. Neighbors in Harlem reportedly smelled it the night before the explosion, and another report of heavy gas stench in the morning had crews from Con Edison en route to the scene. (They arrived just minutes before the blast.) Residents of San Bruno also reported smelling gas in the days before disaster struck.

If a leak is substantial enough, you might actually see the gas before it undergoes combustion. Watch this interview with firefighters in Lafayette, Indiana, who saw vapors rise from the street as they responded to a nasty gas fire spawning explosions all over the place:

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Are tragedies like these impossible to prevent?

Hard to say. The task of replacing the nation's aging gas pipes can seem like excavating the root system of a Giant Redwood with tweezers and a scalpel. Following San Bruno, PG&E actually ran pressurized water through its lines to detect and fix a bunch of leaks. But that's a drop in the bucket toward solving the national problem. And there will always be construction workers who don't know about underground pipes and dig into them (or know about them, and still manage to dig into the dang things).

The U.S. government has looked into technology that could help prevent these awful disasters – a gas-detection platform based on a drone, an "artificial nose" that detects fainter traces of gas than the sniffer devices now used by utilities workers. However, the gas industry still mostly relies on public reports of bad smells when responding to leaks. And though there are gas alarms available for household use, Lavezzo doubts whether they'll ever find a wide audience.

"When you hit something of [San Bruno's] scale, then it raises the cautiousness of people," he says. "But you know what – when it's been two years or more afterward and people are starting to rebuild, they become very lax about that stuff."

Top image: Emergency crews respond to an explosion that leveled two apartment buildings in the East Harlem neighborhood of New York, Wednesday, March 12, 2014. (Jeremy Sailing / Associated Press)